Changes:
* These still use the old hotkeys - Add (Shift-L), Remove (Alt-L), Rename (Ctrl-Shift-L)
* Outliner now shows PoseLib entry. Todo still is to use a different icon for this?
Notes:
* The code is now much simpler in many places :)
* Add and Rename operators require a string as input to set a new name for the Pose concerned. For now, I've just added a prop for this, which will hopefully be able to be filled in at some point.